This is a count of attempts made against the storage bitmap cache, i.e., all free-space allocation lookups whether or not they hit the cache. An administrator pairs this with vmsFileBitmapHit to compute the hit ratio for disk free-space lookups. For example, a surge in vmsFileBitmapAttempt during a large file copy operation without matching hits would indicate the bitmap cache is being overwhelmed by the volume of new allocation requests.